Co,Ba,K/ZrO2 coated onto metallic foam (AISI 314) as a structured catalyst for soot combustion: Catalytic activity and stability Original Research Article

This work presents results on the catalytic activity and stability in the diesel soot combustion of a structured catalyst composed of a Co,Ba,K/ZrO2 layer coated onto a metallic foam (AISI 314). The washcoated ZrO2 layer, mainly of tetragonal structure, adopted the form of mosaics (flakes) with interconnected surface cracks. After the impregnation of the active components, the fresh catalyst was constituted by a complex mixture of phases originated in the chemical compositions of both the metallic foam and the active ingredients, the main crystalline phases detected being Cr2O3, FeCr2O4, Mn1.5Cr1.5O4, ZrO2, BaCO3, K2CrO4 and BaCrO4. The performance of the structured catalyst was maintained within a wide range of soot:catalyst ratios, which is an important factor to be considered for practical applications due to the variable soot amounts that are released by the engine during its operation under different conditions. The stability of the catalyst was evaluated under loose contact conditions during 120 h of time-on-stream, showing that the catalytic activity remained practically constant. The characterization of the fresh and used catalysts indicated the migration of both Co and K towards more exposed positions after TPO runs, which could be a positive factor given the oxidizing properties of Co oxides and the improvement of the soot-to-catalyst contact given by K species. However, a longer duration or severe ageing temperatures might lead to sintering and loss of soot oxidation ability.